opengl: libGL can just be symlinks instead of fake pkgconfig files

The disk-cache-key can't use "drivers" as it creates a loop.

pkgs/opengl/default.nix

@@ -43,6 +43,7 @@ in {
 
   mesa_glxgallium = mesa.overrideAttrs (attrs: {
     mesonFlags = attrs.mesonFlags ++ [
+      "-Ddisk-cache-key=${placeholder "out"}"
       "-Dglx=gallium-xlib"
       "-Ddri-drivers="
       "-Dgallium-drivers=swrast"
@@ -50,13 +51,23 @@ in {
       "-Dgallium-nine=false"
     ];
 
-    # No dri drivers so need to drop all the "drivers" output code (ignoring vulkan for now)
-    outputs = [ "out" "dev" "osmesa" ];
-
     postInstall = ''
+      # move drivers (just vulkan in our case and doesn't avoid LLVM)
+      mkdir -p $drivers/lib
+      mv -t $drivers/lib $out/lib/libvulkan_*
+
       # move libOSMesa to $osmesa, as it's relatively big
       mkdir -p $osmesa/lib
         mv -t $osmesa/lib/ $out/lib/libOSMesa*
+
+      # move vendor files
+      mv $out/share/ $drivers/
+
+      # Update search path used by Vulkan (it's pointing to $out but
+      # drivers are in $drivers)
+      for js in $drivers/share/vulkan/icd.d/*.json; do
+        substituteInPlace "$js" --replace "$out" "$drivers"
+      done
     '';
     postFixup = "";
   } );
@@ -70,35 +81,23 @@ in {
 
     nativeBuildInputs = [ xorg.lndir ];
 
-    # Use stub libraries from mesa_glxgallium and libglvnd and headers from lib_noglu
+    # Use stub libraries from mesa_glxgallium and libglvnd
     buildCommand = ''
       mkdir -p $out/lib
       lndir -silent ${mesa_glxgallium.out}/lib $out/lib
       lndir -silent ${libglvnd.out}/lib $out/lib
 
-      mkdir -p $dev/{,lib/pkgconfig,nix-support}
-      echo "$out" > $dev/nix-support/propagated-build-inputs
-      echo ${autoVirtualGLHook} >> $dev/nix-support/propagated-build-inputs
-      ln -s ${mesa.dev}/include $dev/include
+      mkdir -p $dev/include
+      lndir -silent ${mesa_glxgallium.dev}/include $dev/include
+      lndir -silent ${libglvnd.dev}/include $dev/include
 
-      genPkgConfig() {
-        local location="$1"
-        local name="$2"
-        local lib="$3"
+      mkdir -p $dev/nix-support
+      echo "${autoVirtualGLHook} ${mesa_glxgallium.dev} ${libglvnd.dev} $out" \
+        > $dev/nix-support/propagated-build-inputs
 
-        cat <<EOF >$dev/lib/pkgconfig/$name.pc
-      Name: $name
-      Description: $lib library
-      Version: ${mesa.version}
-      Libs: -L$location/lib -l$lib
-      Cflags: -I${mesa.dev}/include
-      EOF
-      }
-
-      genPkgConfig ${mesa_glxgallium.out} gl GL
-      genPkgConfig ${libglvnd.out} egl EGL
-      genPkgConfig ${mesa_glxgallium.out} glesv1_cm GLESv1_CM
-      genPkgConfig ${mesa_glxgallium.out} glesv2 GLESv2
+      mkdir -p $dev/lib/pkgconfig
+      ln -st $dev/lib/pkgconfig ${mesa_glxgallium.dev}/lib/pkgconfig/{gl,GL,glesv1_cm,GLESv1_CM,glesv2,GLESv2}.pc
+      ln -st $dev/lib/pkgconfig ${libglvnd.dev}/lib/pkgconfig/{egl,EGL}.pc
     '';
   };
 }